The invention refers to a charged compressor for compressed air supply of a commercial vehicle, with a piston chamber, a dead space and a valve unit for engaging the dead space.
The invention furthermore refers to a method for controlling a charged compressor for compressed air supply of a commercial vehicle, with a piston chamber, a dead space and a valve unit for engaging the dead space.
Modern commercial vehicles often have compressed air-operated sub-systems such as a compressed air-operated service brake and pneumatic suspension, which is why a compressed air supply unit, which includes a compressor, is customarily integrated into the commercial vehicle. Furthermore, the commercial vehicle normally has an internal combustion engine which for efficiency reasons is often equipped with a turbocharger.
There are basically now two different possibilities for the compressor for taking in ambient air. One possibility is to induct uncompressed air upstream of the turbocharger, wherein ambient air can also be simply inducted, whereas the other possibility is to branch off already precompressed air downstream of the turbocharger, and ideally downstream of a charge-air cooler which is associated with the turbocharger. As a result of inducting air which is already compressed by the turbocharger, a greatly increased air throughput ensues in the compressor, especially at higher engine speeds and high engine loads. At low engine speeds, however, an increased air delivery can barely be established. The typical turbocharger designs, which at low engine speeds and low loads build up hardly any useful charging pressure, are responsible in this case.
It is furthermore disadvantageous that very large valves are required inside the compressor in order to be able to cope with the high volumetric flows which occur at high charging pressures. When using conventional valves, peak pressures of 20 to 30 bar can occur, which lie significantly above the peak pressures of 12 to 18 bar which occur without turbocharging. Alternatively, it is possible to reduce the maximum compression of the compressor by use of a permanently available dead space which, however, has a disadvantageous effect upon the air delivery of the compressor, especially in the case of low charging pressure, and would further reduce the air delivery in this range. Furthermore, it is to be noted that the commercial vehicle often has an increased air requirement at low engine speeds. Container change operation and stopping-point air requirements of a bus, are examples of where there is an increased air requirement at low engine speeds.
The invention is based on the object of providing a charged compressor which minimizes or eliminates the stated disadvantages.
This and other objects are achieved by a charged compressor for compressed air supply of a commercial vehicle with a piston chamber, a dead. space, and a valve unit for engaging the dead space. The valve unit is formed such that the air volume which is delivered by the charged compressor can be reduced to a value which differs from zero by engaging the dead space.
Advantageous designs and developments of the invention are also described herein.
The invention builds on the generic-type charged compressor by forming the valve unit such that the air volume, which is delivered by the charged compressor, can be reduced to a value which differs from zero by engaging the dead space. By engaging (utilizing or activating) the dead space and reducing the delivered air volume which is associated with it, the peak pressures inside the charged compressor, which occur during a compression phase, are reduced. The valves can therefore be designed for lower volumetric flows, wherein at the same time a permanently available dead space can be dispensed with. Furthermore, the components of the crank drive can remain largely unreinforced.
Provision can advantageously be made in this case for the valve unit to include a plurality of valves which can be individually operated. The engaging of the dead space is customarily carried out by operating a valve unit which opens a connection between the piston chamber and the dead space in the form of a defined valve cross section. Via this defined valve cross section, the charged compressor breathes air into the dead space during the compression phase. In addition to the dead space volume, the valve cross section of the opened connection is of significance since this determines the flow resistance for the air. A plurality of valves which can be individually operated therefore enable an increasing of the valve cross section which is adapted to the charging pressure, or a reducing of the flow resistance.
Furthermore, provision can beneficially be made for the dead space to include a plurality of separate volumes which can be individually engaged by the valve unit. The engaging of a further dead space volume enables a further reduction of the peak pressures which occur in the charged compressor, if required.
Alternatively, provision can be made for the valve unit to include a valve which can be operated in at least two stages. Also, with a valve which can be operated in at least two stages, the opened valve cross section between the piston chamber and the dead space can be adjusted in a need-based manner, which is why in this way the peak pressures which occur in the charged compressor can also be reduced in stages.
Provision can especially be made for the air volume, which is delivered by the charged compressor, to be reduced to zero by engaging the dead space. If the valve cross section between the piston chamber and the dead space which can be opened by the valve unit is large enough, and at the same time the volume of the dead space is sufficient, then the delivery pressure which can be achieved by the charged compressor can be lowered below the pressure which is required for delivery of an air volume. In this state, the charged compressor delivers no more air volume and correspondingly requires less energy since it performs less work. In this way, a system for energy economy can be realized.
Furthermore, provision can be made for a clutch, which is associated with the charged compressor, to be suitable for disengaging the charged compressor from the engine. As a result of the total breaking of the connection between compressor and engine, the air delivery, and the load of the compressor which is related to it, is reduced to zero.
The inventive method reduces the air volume, which is delivered by the charged compressor, to a value which differs from zero by engaging the dead space. In this way, the advantages and characteristics of the compressor according to the invention are also put into effect within the scope of a method. This also applies to the especially preferred embodiments of the method according to the invention which are disclosed in the following.
This is usefully developed by the delivered air volume being influenced by changing an altogether open valve cross section of the valve unit between the dead space and the piston chamber.
Furthermore, provision can be made for the air volume, which is delivered by the charged compressor, being reduced to zero by engaging the dead space. Provision can also usefully be made for at least one condition for engaging the dead space being fulfilled only during an acceleration phase of the commercial vehicle.
Provision can especially be made for the engaging of the dead space to be carried out in dependence upon at least one of the following values: engine speed, turbocharger speed, charging pressure of the turbocharger, engine load, and air requirement of the commercial vehicle.
The charging pressure of the turbocharger or the turbocharger speed, or the engine speed and the engine load, may be used as a decision base as to whether engaging the dead space for lowering peak pressures, which occur in the charged compressor, is advisable. Furthermore, the air requirement of the commercial vehicle can be used as a criterion for engaging the dead space. If the commercial vehicle has sufficient compressed air, the charged compressor can be transferred into an energy-economizing state independently of other values.
Provision can advantageously be made for a clutch, which is associated with the compressor, to be engaged to disengage the compressor from the engine. In this case provision is usefully made for at least one condition for engaging the clutch to be fulfilled only during an acceleration phase of the commercial vehicle.
Provision can especially be made for the engaging of the clutch to be carried out in dependence upon at least one of the following values: engine speed, turbocharger speed, charging pressure of the turbocharger, engine load, and air requirement of the commercial vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.